Wideband Code Division Multiple Access (Wideband Code Division Multiple Access, “WCDMA” for short) is a radio communications technology developed by the 3rd Generation Partnership Project (3rd Generation Partnership Project, “3GPP” for short). This technology is now put into wide use and keeps evolving over time. In the WCDMA Rel-5 and a later release, a high speed packet access (High Speed Packet Access, “HSPA” for short) technology is introduced to support higher-speed data service transmission. Currently, the HSPA is evolving towards HSPA+, to provide support for a higher-order multi-input multi-output (Multiple Input Multiple Output, “MIMO”) technology and key technologies such as aggregation of more carriers.
A new project was initiated at the 53rd conference of the 3GPP radio access network (Radio Access Network, “RAN” for short) to discuss downlink 4-antenna MIMO with the purpose of further improving a cell throughput. In a downlink 2Tx MIMO system that is already supported, a primary common pilot channel (Primary Common Pilot Channel, “P-CPICH” for short) and a secondary common pilot channel (Secondary Common Pilot Channel, “S-CPICH” for short) are used to support channel state information (Channel Status Information, “CSI”) estimation and data demodulation. In downlink 4Tx MIMO, more S-CPICH channels may be supported to perform CSI estimation; and a scheduled non-precoded pilot (Scheduled non-precoded pilot, which is also called a scheduled pilot or a demodulated common pilot) is supported to perform data demodulation. The scheduled non-precoded pilot is sent only at the time of data transmission. Power of the scheduled non-precoded pilot is generally higher than that of a common pilot sent on an antenna 3 and an antenna 4, which helps a user equipment (User Equipment, “UE” for short) to perform more accurate channel estimation by using the scheduled non-precoded pilot, and therefore obtain better data demodulation performance.
There are times when scheduled non-precoded pilot is of little help to enhancing performance of a 4Tx MIMO UE, for example, when a signal to interference plus noise ratio (Signal to Interference plus Noise Ratio, “SINR” for short) of the UE is relatively low; therefore, in this case, the scheduled non-precoded pilot may not be sent, so as to reduce interference to other UEs. Especially, for a terminal incapable of 4Tx MIMO, the scheduled non-precoded pilot is nothing but interference to the terminal, and performance of the terminal can be improved to some extent if the scheduled non-precoded pilot is not sent.
It is agreed by the 3GPP standards body that the scheduled non-precoded pilot may be activated or deactivated by using shared control channel for high speed downlink shared channel (Shared Control Channel for High Speed Downlink Shared Channel, “HS-SCCH” for short) signaling. On a network, if it is determined, for example, according to the fact that a 4Tx MIMO UE has a relatively low signal-to-noise ratio, that the scheduled non-precoded pilot may not be sent, the scheduled non-precoded pilot may be deactivated by using the HS-SCCH signaling; conversely, if it is determined that the scheduled non-precoded pilot needs to be sent, the scheduled non-precoded pilot may be activated by using the HS-SCCH signaling.
At present, when downlink 4Tx MIMO is configured for a cell, a UE initially does not know whether the scheduled non-precoded pilot is activated or deactivated. It may be beneficial for the UE to learn whether the scheduled non-precoded pilot is activated or deactivated, because by doing so, the UE can use the scheduled non-precoded pilot, if present, to improve precision of 4Tx MIMO data detection. Whether the scheduled non-precoded pilot is activated is decided by a base station, and is a typical cell-level parameter, and may be determined according to conditions of multiple UEs. Therefore, when a UE is configured to operate in a downlink MIMO state by a radio network controller (Radio Network Controller, “RNC” for short), the scheduled non-precoded pilot may be either activated or deactivated.
A UE cannot determine, according to an actual state of a base station, whether the scheduled non-precoded pilot is in an activated or deactivated state. Almost each time when downlink 4Tx MIMO is configured for a UE, a base station needs to send HS-SCCH signaling to notify the UE of scheduled non-precoded pilot state, either activated or deactivated. Therefore, a large amount of HS-SCCH signaling is required to perform such function, which increases overheads of physical-layer dynamic signaling. In addition, after sending the HS-SCCH signaling, the base station needs to wait for the UE to send an acknowledgment (Acknowledgment, “ACK” for short) before sending scheduling data to the 4Tx MIMO UE, which results in a scheduling delay.